System and method for efficiently using channel unit hardware to provide multiple narrowband channels overlaid on a single wideband channel in a satellite communications network

ABSTRACT

A system and method for the efficient use of satellite radio modems and satellite bandwidth is disclosed. In the system and method, a satellite radio modem is used for PRACH requests, each PRACH request occupying 31.25 kHz in a packet data transfer channel. The packet data transfer channels can be either 125.0 kHz or 156.25 kHz. Therefore, four PRACH requests can be transmitted in any one packet data transfer channel. The packet data transfer channels are broken into eight time slots, and one time slot in each channel (either the odd frame or even frame) is dedicated to a PRACH request. A satellite radio modem for PDCH transfers is dedicated for each channel. The satellite radio modem assigned to receive the four PRACH requests is timeshared over 16 channels, thereby reducing the amount of satellite radio modems that would otherwise have been needed, had the PRACH request transmissions utilized a dedicated modem for each PRACH request, for each channel.

FIELD OF THE INVENTION

The present invention relates to a system and method for efficientlyusing modems in satellite communications. More particularly, theinvention relates to a method and system for efficiently utilizing wideand narrowband packet data transmission channels through the sharing ofwide and narrowband modems.

BACKGROUND OF THE INVENTION

Great advances in the field of wireless communications have been madeover the past twenty years, and continue to be made. These advances bothimprove the quality of communication, e.g., the clarity and reliabilityof communication, and improve the geographic coverage of such wirelesscommunications. As industry strives to provide a wireless communicationscapability that covers the entire globe, factors such as economicviability dictate that space-based transceivers be employed as opposedto ground infrastructure. However, systems that employ groundinfrastructures remain technologically advantageous and economicallypreferable in identified population centers where a great deal ofbandwidth is required in a relatively small area. Thus, two types ofwireless communication, i.e., ground infrastructure cellular, andspace-based satellite systems have emerged.

Modems are well-known in the art of digital communications. The wordmodem is a contraction of the words modulator and demodulator. A modemis typically used to send digital data over in transmission line. Thesending modem modulates the data into a signal that is compatible withthe transmission line and the receiving modem de-modulates the signalback into digital data. Wireless modems are frequently used in cellularand satellite communication systems for converting data into radiosignals and visa-versa.

Modems utilize any number of a different modulation schemes thattransmit digital data. For example, modems used in transmitting digitaldata over telephone lines would use frequency shift keying (FSK), phaseshift keying (PSK), and quadrature amplitude modulation (QAM). Thesetechniques allow an incredible amount of information to be inserted intothe relatively small bandwidth available on normal voice grade phonelines. In satellite communication systems, however, much higher speedsof communication are available through the use of these and othersophisticated modulation techniques.

As discussed above, because of increased use of the Internet, the use ofmodems has risen substantially. In the early stages of Internet use, theInternet was primarily utilized through conventional landlines, i.e.,plain old telephone service (POTS) lines. However, as use of theInternet became more prolific, and users demanded greater accessibility,means for wireless Internet service became established and is now fairlycommon. However, in many places of the world, where cellular wirelesscommunication systems are not in place to provide telephone or Internetaccess, satellite communication systems can be used.

FIG. 1 is a block diagram of a satellite telecommunication system. InFIG. 1 satellite 2, located in space 4, transmits via spot beams 8A–8C,data and voice information. Each spot beam 8 comprises not more than 75communication channels, suitable for packet data transfer, numbered 01to 75. Each channel can be either 125.0 kHz or 156.25 kHz, as discussedin greater detail below.

The Internet operates in a packet switched environment, as opposed tothe circuit switched environment of normal landline (and even mostwireless) telephone systems. “Circuit Switched” is the most familiartechnique used to build a communications network. It is used forordinary telephone calls. Circuit switching means that each user hassole access to a circuit (functioning equivalent to a pair of copperwires) during network use. Essentially, it is a direct link, through thepaired copper wires, and a network between two end points. “PacketSwitching” however is somewhat different then circuit switching. PacketSwitching is similar to message switching using short messages. Anymessage exceeding a network defined maximum length is broken into shortunits, known as “packets” for transmission. The packets, each with anassociated header, are then transmitted individually through thenetwork. In a packet system a number of users may simultaneously receivethe transmitted data. Each packet is individually addressed, which ishow they get to the correct recipient. In essence, there is no completeddirect connection between the sending and receiving units. It ispossible, and quite frequently it does happen, that an outgoing link maynot be available in which case a packet is placed in a queue until thelink become free to use. A packet network is formed by links whichconnect packet network equipment.

Wireless packet data systems are being developed based on the GeneralPacket Radio Service (GPRS) standard. This has been enhanced forsatellite operation, the enhancement being named Geo-Mobile Packet RadioService (GMPRS) standard. GMPRS is an advanced data transmission modethat does not require a continuous connection to the Internet, as with astandard home modem. Instead, a system that employs GMPRS uses thenetwork only when there is data to be sent, which is more efficient inwireless communication systems, where power and spectrum are scarceresources. The base frequency bandwidth for packet data transfer iseither 156.25 kilohertz or 125 kilohertz depending on the configurationused. In addition to packet data transfer (a channel allocated forpacket data transfer is referred to as a packet data channel, or PDCH),the same satellite channels are used for packet random access channel(PRACH) requests. A PRACH request is used by a remote terminal torequest an allocation of resources (i.e., the channel) in order totransfer data from the terminal. Since the payload requirements for aPRACH request is significantly lower than the packet data transfer, thePRACH occupies only 31.25 kHz. In order to make efficient use of thebandwidth, the modified air interface allows multiply PRACH's to occupythe same space as a single PDCH (in either the 156.25 kilohertz channel,or the 125 kilohertz channel). This is explained with reference to FIG.2.

FIG. 2 illustrates a first wideband channel for transferring packet dataand random access channel requests in a satellite communication systemutilizing the GMPRS standard. As seen in FIG. 2, there is an odd frame201 and an even frame 202. In odd frame 201 and even frame 202, thereare eight time slots of 5 milliseconds a piece. Therefore, each channelframe transmission time is 40 milliseconds. The time slots are denotedtime slot A (TS-A), time slot B (TS-B), etc. In FIG. 2, the transmissionbandwidth is 125.00 kHz. In FIG. 2, TS-A and TS-C through TS-H of oddframe 201 are dedicated to packet data channel (PDCH) transfers. TS-B,however, is dedicated for a PRACH. There are four PRACH transmissions(PR-1, PR-2, PR-3 and PR-4), each occupying 31.25 kilohertz ofbandwidth. In even frame 202, however, there is no PRACH transmission.PRACH transmissions occur in an odd frame or an even frame, but notboth, in any given channel.

FIG. 3 illustrates a second wideband channel for transferring packetdata and random access channel requests in a satellite communicationsystem utilizing the GMPRS standard. Although the transmission bandwidthis 156.25 kHz, it can been seen in odd frame 301, the top frequency bandof 31.25 kilohertz is crossed-hatched to represent that no datatransmission occurs in that frequency band. Thus, all transmissionsoccur around the frequency carrier signal from 0–125 kilohertz. In evenframe 302, the first 31.25 kHz is cross hatched to represent that nodata transmission is occurring in that frequency band. In FIG. 3, TS-Cof even frame 302 contains the PRAQCH transmission.

Normally, satellite radio modems (SatMods) are assigned to channels on afixed basis. SatMod assignment is performed by a device call the PacketResource Management System (PRMS). When a new channel (or sub-band) isassigned, the PRMS looks through a list of available PRACH SatMods, andassigns the according to which slots are free. As has been discussed,the wideband packet data channels (PDCH) are periodically overlaid withmultiple narrowband channels. However, if conventional techniques wereused to receive a PRACH transmission as with a PDCH transmission, itwould be necessary to provide up to five times the modem hardware thenis needed for data transfer alone, at great expense.

FIG. 4 illustrates a first example of an inefficient allocation ofsatellite radio modems for transferring PDCH and PRACH transmissionsutilizing the GMPRS standard. In FIG. 4, SatMod 1 has been assigned tochannel 50. It will receive all the packet data transfers (PDCH).However, SatMods 2–5 have been assigned to receive one PRACHtransmission each. SatMod 1 can be used for channel 50 odd frame, aswell (but not at the same time), but no other channel. SatMods 2–5 canlikewise be used only for channel 50 odd and even frames. This is thesame for all 75 channels. Therefore, in 75 channels, 75 PDCH SatMods areneeded, and 300 PRACH SatMods (75 channels×4 PRACH SatMods/channel=300PRACH SatMods), for a total of 375 SatMods. The significant component ofa SatMod is a high-speed digital signal processor (DSP) that iscontained in the SatMod. A SatMod will be considered to be one DSP.

FIG. 5 illustrates a second example of an inefficient allocation ofsatellite radio modems for transferring packet data and random accesschannel requests utilizing the GMPRS standard. The allocation of SatModsin FIG. 5 is only slightly more efficient than in FIG. 4. Here, PDCHSatMod 1 is used for PRACH (PR) SatMod for PR-4 (in TS-B), while SatMods2–4 are used in PR-1, PR-2 and PR-3, respectively. In this example,therefore, for 75 channels, 75 PDCH SatMods are needed, and 225 PRACHSatMods are used (75 channels×3 PRACH SatMods/per channel=225 PRACHSatMods) for a total of 300 SatMods.

FIG. 6 illustrates of a third example of an inefficient allocation ofsatellite radio modems for transferring packet data and random accesschannel requests utilizing the GMPRS standard. FIG. 6 represents aninefficient allocation of both SatMods and bandwidth resources. In FIG.6, SatMod 1 will be used for PDCH transfers in channel 50, even and oddframes. In this case, though, only one PRACH is transmitted, PR-4,alleviating the need for any additional SatMods, because for eachchannel, the one SatMod for the channel can easily handle the smallerbandwidth PRACH, as well as the much higher bandwidth PDCH transfers. Ata minimum, therefore, only 75 SatMods need be used; but, instead ofcompletely utilizing the bandwidth capacity of a time slot in eachchannel's even and odd frame, only 31.25 kHz (PR-4) of the PRACHtimeslot is being used. Alternatively, a single PRACH SatMod can handlethe PRACH (in this example PR-4) for each channel, thereby doubling thenumber of SatMods to 150. In both the 125.0 kHz and 156.25 kHz widebandchannel, 75% of the PRACH channel's time slot capacity is wasted.

Thus, there is a need for efficiently using modems in a satellitecommunication system that transfers packet data and random accesschannel requests utilizing the GMPRS standard, and a need for efficientutilization of channel bandwidth in such a system.

SUMMARY OF THE INVENTION

It is therefore a general object of the invention to provide a novelsystem and method to efficiently utilize channel unit hardware in asatellite based communications system that will obviate or minimizeproblems of the type previously described.

It is therefore an additional object of the invention to efficiently usemultiple 125.0 kHz data channels by multiplexing narrowband modems overmultiple packet data channels for PRACH, while dedicating a minimum ofwideband modems for packet data transfer in a satellite communicationsystem utilizing the GMPRS standard.

It is therefore a further object of the invention to efficiently usemultiple 156.25 kHz data channels by multiplexing narrowband modems overpacket data channels for PRACH, while dedicating a minimum of widebandmodems for packet data transfer in a satellite communication systemutilizing the GMPRS standard.

It is yet another object of the invention to implement a system andmethod utilizing wideband modems, some in a dedicated fashion and somein a multiplexed fashion, to efficiently and economically use widebandmodems for transferring packet data and packet random access channelrequests in a satellite communication system utilizing the GMPRSstandard for packet data transfers.

It is therefore an object of the invention to efficiently use multiple125.0 kHz data channels by multiplexing narrowband modems over multiplepacket data channels for PRACH, while dedicating a minimum of widebandmodems for packet data transfer in a satellite communication systemutilizing the GMPRS standard.

It is therefore a further object of the invention to efficiently usemultiple 156.25 kHz data channels by multiplexing narrowband modems overmultiple packet data channels for PRACH, while dedicating a minimum ofwideband modems for packet data transfer in a satellite communicationsystem utilizing the GMPRS standard.

It is yet another object of the invention to implement a system andmethod utilizing wideband modems, some in a dedicated fashion and somein a multiplexed fashion, to efficiently and economically transferpacket data and random access channel requests in a satellitecommunication system utilizing the GMPRS standard for packet datatransfers.

A system is shown for transmitting data and control information in asatellite telecommunication system, which comprises a plurality oftransmission channels, each transmission channel comprised of aplurality of time slots and having a first bandwidth and at least one ofthe time slots dedicated to transmitting control information, while theremainder of the time slots transmit data information. The controlinformation time slot transmission is divided into a plurality oftransmissions of a second bandwidth. The system further contains aplurality of first type modems, each first type modem configured anddedicated to receive the data information from a separate transmissionchannel, and a second type modem configured to receive the controlinformation from each of the plurality of transmission channels in atime shared mode.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the invention are setforth in the appended claims. The invention itself, however, as well asother features and advantages thereof will be best understood byreference to the detailed description of the specific embodiments whichfollows, when read in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a block diagram of a satellite communication system;

FIG. 2 illustrates a first wideband channel for transferring packet dataand random access channel requests in a satellite communication systemutilizing the GMPRS standard;

FIG. 3 illustrates a second wideband channel for transferring packetdata and random access channel requests in a satellite communicationsystem utilizing the GMPRS standard;

FIG. 4 illustrates a first example of an inefficient allocation ofsatellite radio modems for transferring packet data and random accesschannel requests utilizing the GMPRS standard;

FIG. 5 illustrates a second example of an inefficient allocation ofsatellite radio modems for transferring packet data and random accesschannel requests utilizing the GMPRS standard;

FIG. 6 illustrates a third example of an inefficient allocation ofsatellite radio modems for transferring packet data and random accesschannel requests utilizing the GMPRS standard;

FIG. 7 is a block diagram of a first satellite radio modem used ineither a first or second embodiment of the invention;

FIG. 8 illustrates a first embodiment of the invention; and

FIG. 9 illustrates a second embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The various features of the preferred embodiment will now be describedwith reference to the figures, in which like parts are identified withsame referenced characters.

FIG. 7 is a block diagram of a first satellite radio modem used ineither a first or second embodiment of the invention. Satellite radiomodem (SatMod) 700 illustrated in FIG. 7 is defined as containing 1digital signal processor, DSP-1 702. DSP-1 702 has a bandwidth of 156.25kHz. Therefore, each modem is capable of receiving four PRACH transfers(4×31.25 kHz=125.0 kHz) or one PDCH transfer. However, in addition tothe DSP, SatMod 700 requires additional hardware (power supplies,internal processing capabilities, communications buses, input/outputhardware, etc), as is well known in the art. These have been omitted forsake of clarity.

FIG. 8 illustrates a first embodiment of the invention. In the firstembodiment of the invention, two groups of SatMods are utilized. Thefirst group is allocated to a PDCH transmissions. The second group isallocated for PRACH use, but shared over multiple (16) channels. Thisaccommodation of assigned and timeshare satellite radio modems allowsmaximum bandwidth efficiency at minimum equipment usage.

In FIG. 8, 4 SatMods 700 are assigned as a PRACH SatMod 802, each onecapable of receiving one PRACH transmission for not only one channel,but for fifteen others, for a total of sixteen channels. A packetresource management system (PRMS) assigns the PRACH SatMods for eachchannel as it comes into use. All channel transmissions are synchronizedby the PRMS. As the first channel is assigned, a group of four SatModsis assigned to the channel for PRACH use, in the next available timeslot. When another channel is requested, the four SatMods are assignedto the channel for PRACH use, but in the next available time slot. Thetime slot assignments begin with the odd frame, and then the even frame.

In FIG. 8, channel 50 is the first to be assigned for PDCH and PRACHuse. Since no other channel is in use, time slot A will be used forPRACH transmissions and SatMod 802, which contains SatMods (1–4) (thisis for purposes of illustration only, of course; the physicalconfiguration of the SatMods may be different dependant upon thecircumstances of the design of the satellite system; here, the first 4SatMods are grouped together, numbered 1–4, and given element number 802in FIG. 8. This same convention is used in the discussion regarding FIG.10).

SatMod (5) 804 is assigned for PDCH transmissions. The PRMS assigns timeslot A for PRACH use, and time slots B–E for PDCH use. Since this wasthe first channel to be assigned, only odd frame 820 has PRACH SatModsassigned to it. Even frame 822 is dedicated solely to PDCH use, andSatMod (5) 804 will accommodate those transmissions.

Eventually, the system requires additional PDCH and PRACH transmissioncapability, and channel 51 is assigned next. Because all channeltransmissions are synchronous, the next available time slot will beassigned for PRACH use. It is not necessarily the case that it be thenext sequential time slot, as channel use might be sporadic, and somechannels are used for different periods of time, but, for purposes ofthis discussion, the next available time slot is the next sequentialtime slot. Thus, time slot B of odd frame 820 will be used by SatMods(1–4) for PRACH transmissions. Therefore, for the first 5 millisecondsof channel transmission, PRACH SatMods (1–4) 802 tune to channel 50during time slot A and then tune to channel 51 during time slot B, forthe next 5 milliseconds, and the PRACH transmissions contained therein.

It also might be the case that there are less than four PRACHtransmissions occurring. But up to four PRACH transmissions can beaccommodated in a time slot, as previously discussed. Also, aspreviously discussed, even frame 822 of channel 51 has no PRACHtransmissions, only PDCH transmissions, and this is why there are noPRACH SatMods shown corresponding to channel 51, even frame 820. Whenanother channel must be assigned (and presuming channels 50 and 51 arestill in use) the PRMS can use any unassigned time slot, i.e., not timeslots A and B, as these have already been assigned for PRACH use bychannels 50 and 51, respectively. This process continues until all thetime slots of the odd channel are utilized, and in channel 57 (theeighth channel) time slot H is being used for PRACH transmissions, andtime slots A–G are used for PDCH transmissions.

Once all eight time slots of the odd frames of the selected channelshave been assigned for PRACH transmissions and thus SatMods (1–4) 802,the time slots for even frames of selected channels will be used. Thenext available channel might be channel 58, and time slot A of evenframe 826 is assigned for PRACH use, with SatMods (1–4) 802. Time slotsB–H of even frame 826 of channel 58 will carry PDCH transmissions. Oddframe 824 of channel 58 is dedicated to PDCH use, and SatMod (13) 810will be used for that purpose. This continues until, in a group of 16channels (and again, not necessarily sequential channels), all the timeslots of the odd frames (for a first sub-group) of eight channels havebeen assigned for PRACH use and all the time slots of the even frames(for a second sub-group) of eight channels have also been assigned forPRACH use.

Thus, for any group of 16 channels (in FIG. 8, 16 sequentially numberedchannels), a total of 20 SatMods will be used: SatMods 1–4 for PRACH useacross all 16 channels, and SatMods 5–20 for PDCH use. This means 1.25SatMods are needed for each channel in the configuration according tothis embodiment of the invention. Had this not been the case, that is,if a separate group of PRACH SatMods were to be used for each channel, atotal of 80 SatMods would have been necessary, one for PDCH use for eachchannel (16 SatMods) and four for PRACH use for each channel (64SatMods), for a per-channel allocation of 5 SatMods/channel (80/16=5).This represents a tremendous savings in physical hardware, whichcorrelates to a truly significant savings in power use, space and heatradiation requirements.

Table 1, shown below, summarizes the SatMod assignments for the firstgroup of 8 channels, and Table 2 summarizes the SatMod assignments forthe second group of 8 channels. Channels 50–65 are used for exemplarypurposes only. Under the column heading “Transmission Usage” are thedesignations PDCH (packet data transfer) SatMods, which are fixed to onechannel and PRACH SatMods which are time shared between all 16 channels.

TABLE 1 Channel No. Frame Time Slot Transmission Usage SatMod No. 50 O APRACH 1–4 B–H PDCH 5 E A–H PDCH 5 51 O B PRACH 1–4 A, C–H PDCH 6 E A–HPDCH 6 52 O C PRACH 1–4 A, B, D–H PDCH 7 E A–H PDCH 7 53 O D PRACH 1–4A–C, E–H PDCH 8 E A–H PDCH 8 54 O E PRACH 1–4 A–D, F–H PDCH 9 E A–H PDCH9 55 O F PRACH 1–4 A–E, G, H PDCH 10 E A–H PDCH 10 56 O G PRACH 1–4 A–F,H PDCH 11 E A–H PDCH 11 57 O H PRACH 1–4 A–G PDCH 12 E A–H PDCH 12

TABLE 2 58 O A–H PDCH 13 E A PRACH 1–4 B–H PDCH 13 59 O A–H PDCH 14 E BPRACH 1–4 A, C–H PDCH 14 60 O A–H PDCH 15 E C PRACH 1–4 A, B, D–H PDCH15 61 O A–H PDCH 16 E D PRACH 1–4 A–C, E–H PDCH 16 62 O A–H PDCH 17 E EPRACH 1–4 A–D, F–H PDCH 17 63 O A–H PDCH 18 E F PRACH 1–4 A–E, G, H PDCH18 64 O A–H PDCH 19 E G PRACH 1–4 A–F, H PDCH 19 65 O A–H PDCH 20 E HPRACH 1–4 A–G PDCH 20

It is clearly more efficient to timeshare the PRACH request SatMods over16 channels than any of the embodiments shown in FIGS. 4–6. In acomplete satellite communication system, with 75 channels, the totalnumber of SatMods required is as follows:

75 channels×1 PDCH SatMod/channel=75 PDCH SatMods

75 channels×4 PRACH SatMod/16 channels=18.75 PRACH SatMods

This yields a total of 94 SatMods, as compared to the best case of 225SatMods in the most efficient allocation of SatMods (according to FIG.4) and 375 SatMods in the most inefficient allocation of SatMods(according to FIG. 5), when utilizing all 4 possible PRACH requests in atime slot.

FIG. 9 shows essentially the same information as in FIG. 8, except for a156.25 kHz wideband channel.

The present invention has been described with reference to certainexemplary embodiments thereof. However, it will be readily apparent tothose skilled in the art that it is possible to embody the invention inspecific forms other than those of the exemplary embodiments describedabove. This may be done without departing from the spirit of theinvention. The exemplary embodiments are merely illustrative and shouldnot be considered restrictive in any way. The scope of the invention isdefined by the appended claims and their equivalents, rather than thepreceding description.

1. A system for transmitting data and control information in a satellitetelecommunication system, comprising: a plurality of first type modems,each first type modem configured and dedicated to receive the datainformation from a respective one of plurality of separate transmissionchannels, each said transmission channel comprising a plurality of timeslots and having a first bandwidth, at least one of the time slots beingdedicated to transmitting control information, the remainder of the timeslots transmitting data information, and the control information timeslot transmission being divided into a plurality of transmissions of asecond, smaller bandwidth; and a plurality of second type modems,configured to receive the control information from the plurality oftransmission channels in a time shared mode.
 2. The system of claim 1,further comprising that each of the plurality of second type of modemsis dedicated to one of the plurality of control informationtransmissions of a second smaller bandwidth.
 3. The system of claim 1,wherein the transmission channels are configured into an eventransmission frame, and an odd transmission frame.
 4. The system ofclaim 3, wherein the number of transmission channels equals
 16. 5. Thesystem of claim 3, wherein the number of time slots equals eight.
 6. Thesystem of claim 1, wherein the data information and control informationare for use with the Internet.
 7. The system of claim 6, wherein thedata information comprises packet data.
 8. The system of claim 6,wherein the control information comprises packet channel requests. 9.The system of claim 1, wherein the first bandwidth equals 125 kHz. 10.The system of claim 1, wherein the first bandwidth equals 156.25 kHz.11. The system of claim 1, wherein the first type modem comprises adigital signal processor.
 12. The system of claim 1, wherein the secondtype modem comprises a digital signal processor.
 13. A method fortransmitting Internet information in a satellite telecommunicationsystem comprising: transmitting Internet information in a transmissionchannel; and receiving the Internet information in both a first modemand a second modem; and wherein the transmission channel is divided intoan even and odd frame; and wherein the Internet information is comprisedof a first type of information and a second type of information; andfurther comprising: receiving the first type of information in aplurality of first modems, each of the first modems dedicated to aseparate transmission channel; and receiving the second type ofinformation, from a plurality of transmission channels, in a pluralityof second modems in a time shared basis.
 14. The method according toclaim 13, wherein the first type of information is transmitted in afirst plurality of time slots; and the second type of information istransmitted in a second plurality of time slots.
 15. The methodaccording to claim 13, wherein the first type of information is datainformation, and the second type of information is control information.